1. Field of the Invention
The present invention relates generally to optical imaging, and more specifically to endpoint detection in semiconductor manufacturing using pattern recognition technology on the images obtained from optic camera.
2. Description of the Related Art
In the fabrication of semiconductor structures such as integrated circuits, memory cells, and the like, features, structures, and components are defined, patterned, and constructed in a series of manufacturing process steps on semiconductor wafers to create multi-layer integrated structures. During the semiconductor manufacturing process, semiconductor wafers are processed through numerous operations in controlled environments to add layers, and to define, pattern, etch, remove, polish, etc., structures, features and layers. The structures and features formed on the semiconductor wafers are closely monitored and analyzed to precisely determine the endpoint of each process.
One common manufacturing process is plasma etch. In general, during plasma etch, the processing chamber is configured to receive processing gases. The pressure of the process gases within the chamber is controlled in accordance to the requirements of the desired process. Radio frequency (RF) power is applied to one or more electrodes in the processing chamber. Upon applying the desired RF power to the electrode(s), the process gases in the chamber are activated such that a plasma is created. The created plasma is configured to perform the desired etching of the selected layers of a semiconductor wafer. In semiconductor fabrication, plasma etching is commonly used to etch conductive, dielectric and other materials to define features and structures therein or to expose the defined features/structures.
During the etching process, various tools/technologies are used to perform in-situ monitoring and analysis of the conditions within the plasma chamber to determine an end-point for the etching process, so as to prevent over-etching. One such technology for monitoring uses the optical emission spectroscopy (OES). OES is typically used to detect when a structure or layer is exposed during a plasma etch process. To be effective, the OES detection equipment must be able to resolve a change in emission relative to the background plasma. However, as the features/structures reduce in size, it is becoming increasingly difficult to precisely detect change in emission, especially when the etch process is to have very high selectivity to exposed film around the features/structures.
High selectivity is especially relevant in through-silicon via (TSV) reveal process which performs blanket silicon etch with no stop layer. In the TSV reveal process, TSV nodes are exposed by removing silicon from the backside of the wafer to make contact with the bottom of the TSV nodes defined on the wafer and etch the silicon for a desired height. The etching operation for revealing the TSV nodes have to take into consideration the selectivity of the exposed film, such as liner material around the features/structures, in order to preserve the functionality of the TSV nodes. Due to the high selectivity defined for the etch process, it is very hard to detect when the endpoint for the TSV reveal is reached using the OES technique, as no new species are emitted into the plasma, potentially leading to over-etching of the silicon. The over-etching may result in the TSV nodes protruding too much from the silicon bulk with potential damage to the TSV nodes during packaging.
Another technique that is commonly used is the radio frequency (RF) related endpoint technique. In the RF technique, changes in RF parameters, primarily in the Bias RF delivery, are detected when new films are exposed at endpoint. However, for applications, such as the TSV Reveal, the main etch process does not use Bias Power in order to achieve high selectivity to a film layer formed over the features/structures. As a result, no usable changes in RF parameters can be detected when endpoint is reached.
Another technique that is used in determining end point is the fixed-time approach. This approach makes extensive use of pre-etch and post-etch metrology to control the etch process. The fixed time approach, however, has its own drawbacks as the approach is still vulnerable to process variations, such as drift in the etch rate or variation in the incoming wafer film thickness, etc., leading to unnecessary and excess variation in the desired results, such as large variation in the height of the structures/features.
Each of the above described techniques is well known in the art. The RF technique and the OES signal changes offer extremely low signal to noise ratio and have proven to be inadequate for precisely determining end point for etching processes, especially for the ones that do not use stop film.
In light of the foregoing, what is needed is a system that enables precise prediction of end point, especially for TSV reveal etch process that etches blanket silicon without any stop layer. It is in this context that embodiments of the disclosure arise.